I have seen a very predictable scrum, but the tradeoffs with productivity were comical. In this very large corporation, most developers could do most of the tasks in their 2 week sprints in 3 days of actual work. But they don't know if they are going to get 3 days of actual work, or some other team is going to keep master broken for a week. Therefore, your typical sprint involves mostly fictional standup updates, as to make sure that, when things go more than a little too well, the shameful levels of sandbagging aren't visible in jira or in git.

If you ask me, that level of predictability is a poor tradeoff, but hey, it's the same kind of organization that decides that SAFe scrum is a serious methodology.